Strained silicon device manufacturing method

ABSTRACT

A method of manufacturing a microelectronic device includes forming a p-channel transistor on a silicon substrate by forming a poly gate structure over the substrate and forming a lightly doped source/drain region in the substrate. An oxide liner and nitride spacer are formed adjacent to opposing side walls of the poly gate structure and a recess is etched in the semiconductor substrate on opposing sides of the oxide liner. Raised SiGe source/drain regions are formed on either side of the oxide liner and slim spacers are formed over the oxide liner. A hard mask over the poly gate structure is used to protect the poly gate structure during the formation of the raised SiGe source/drain regions. A source/drain dopant is then implanted into the substrate including the SiGe regions.

CROSS-REFERENCE

This application is related to U.S. patent Ser. No. 10/810,950, filed Mar. 25, 2004, the disclosure of which is hereby incorporated by reference.

BACKGROUND

An integrated circuit (IC) is formed by creating one or more devices (e.g., circuit components) on a semiconductor substrate using a fabrication process. As fabrication processes and materials improve, semiconductor device geometries continue to decrease in size since such devices were first introduced several decades ago. For example, current fabrication processes are producing devices having geometry sizes (e.g., the smallest component (or line) that may be created using the process) of less than 90 nm. However, the reduction in size of device geometries frequently introduces new challenges that need to be overcome.

As microelectronic device geometries are scaled below 65 nm, electrical efficiency becomes an issue that impacts device performance. Microelectronic device performance such as current gain can be significantly affected by the configuration and materials incorporated into microelectronic devices. Therefore, there is an inherent conflict with the configuration and/or the materials used in many of today's microelectronic devices.

Accordingly, what is needed in the art is a microelectronic device and method of manufacture that addresses the above discussed issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart of one embodiment of a method for performing one or more embodiments of the present disclosure.

FIGS. 2–7 are sectional views of a portion of a microelectronic device constructed according to the method of FIG. 1.

FIG. 8 is a sectional view of one embodiment of a microelectronic integrated circuit constructed according to aspects of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the present invention. Specific components and arrangements are described below to simplify the present disclosure by way of example, and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed, nor does it dictate that the referenced component is identical to others with the same reference numeral. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact.

Referring to FIG. 1, a method 10 can be used for manufacturing a microelectronic device according to one or more embodiments of the present invention. For the sake of example, the method 10 will be described with reference to the manufacture of a semiconductor integrated circuit 100, illustrated in FIGS. 2–8. The manufacturing method 10 can be used for the formation of a “graded junction” source/drain doped region in a semiconductor microelectronic device such as a transistor. It is understood that the method 10 can represent only a portion of a process flow, and it is further understood that in some embodiments, certain steps of the method may be rearranged or not performed altogether.

Referring also to FIG. 2, in the present example, the method 10 begins at step 12 for creating a microelectronics device 101. The device 101 includes a substrate 102, isolation regions 104, a gate layer 108, an electrode 110, and a hard mask 111.

The substrate 102 may be a semiconductor substrate, such as one including silicon. The isolation regions 104 may include silicon dioxide (SiO₂), silicon nitride (Si_(x)N_(y)), silicon carbide (SiC), low-k dielectric, and/or other materials. In one embodiment, the isolation regions 104 may be created by etching or otherwise forming a recess in the substrate 102 and subsequently filling with one or more layers of a dielectric.

The gate layer 108, which may be gate oxide, is formed followed by the formation of the bulk gate electrode 110, which may include a layer of polysilicon. In the present example, a hard mask layer 111 resides over the gate electrode 110. The hard mask layer 111 is about 250 Angstroms in thickness (height, as shown in FIG. 2), and may include silicon nitride (Si_(x)N_(y)), silicon dioxide (SiO₂), silicon oxy-nitride (SiON), photoresist, and/or other materials.

At step 14, doped regions 106 a are formed in the substrate 102. In the present embodiment, the doped regions 106 a are lightly doped drain/source (LDD) regions that are implanted relatively shallow into the substrate 102. The LDD regions 106 a can be created by CVD, PECVD, ALD, ion implantation, and/or other processing techniques. For example, the doped regions 106 a may be formed by growing a sacrificial oxide on the substrate 102, opening a pattern for the location of the doped regions 106 a and then using a chained-implantation procedure. Alternatively, the doped regions 106 a may be formed by selective epitaxial growth (SEG).

For the sake of example, the doped regions 106 a include P-type impurities such as boron, boron fluoride, indium, and/or other materials. Formation of the P-type doped regions may include one or more diffusion, annealing, and/or electrical activation processes. A channel region 120 is thereby formed between the two doped regions 106 a. Continuing with the present example, the channel region 120 is a P-channel.

Liners 112 are then formed on the vertical (as illustrated in FIG. 2) sides of the gate electrode 110. In the present embodiment, the liners 112 are L-shaped and include an oxide dielectric layer formed by CVD, PVD, ALD, PECVD, SEG, and/or other processing techniques. Spacers 114 are then formed on the sidewalls of the liners 112. In the present embodiment, the spacers 114 are nitrogen based insulators, such as silicon nitride (Si_(x)N_(y)). In alternate embodiments, the spacers 114 may include silicon oxide (SiO₂), photoresist, and/or other polymers. In the present embodiment, the spacers 114 and the lower portion of the liners 112 are relatively wide, with a width s₁ of about 650 Angstroms.

Referring also to FIG. 3, at step 16 (of FIG. 1), silicon recesses 122 are formed on either side of the spacers 114. In the present example, selected portions of the doped regions 106 a are removed. The portions of the doped regions 106 a located under the liners 112 and spacers 114 remain following the removal of the exposed portions of the doped regions 106 a. The exposed portions of the doped regions 106 a may be removed by silicon etch, chemical etch, plasma etch, or other appropriate method.

Referring also to FIG. 4, at step 18 (of FIG. 1), an epi layer 124 is formed in the recesses 122 of FIG. 3 between the doped regions 106 a and the isolation regions 104. The epi layer 124 may include silicon germanium (SiGe). Other embodiments include silicon carbide (SiC), and/or other epi materials. It is noted that in the present embodiment, SiGe does not accumulate on the hard mask 111 or on the spacers 114. The epi layer 124 is used to make the microelectronic device 101 a “strained silicon” device.

Referring also to FIG. 5, at step 20 (of FIG. 1), the spacers 114 are partially etched, forming “slim” spacers herein designated with the reference numeral 114 a. The slim spacers 114 a are shown having a width s₂, which is less than the width s₁ (FIG. 2). The width s₂ of the slim spacers 114 a may be on the order of about 350 Angstroms. As a result, the lower portion of the liners 112 extend about 300 Angstroms (650−350=300 Angstroms) beyond the slim spacers 114 a. The slim spacers 114 a may be formed by chemical etch, dry etch, plasma etch, and/or other processing techniques. In one embodiment, the slim spacers 114 a are formed by a wet etch of phosphoric acid (H₃PO₄).

The hard mask 111 is also removed, either at the same time that the slim spacers 114 a are formed, or at a different time. The hard mask 111 may be removed by chemical etch, plasma etch, and/or other techniques. For example, the hard mask 111 may be removed by plasma etch, which may include an environment having reactants such as hydrochloric acid (HCl), hydrogen bromide (HBr), sulfur dioxide (SO₂), sulfur hexafluoride (SF₆), perfluorocarbons, and/or other gases.

Referring also to FIG. 6, at step 22 (of FIG. 1), the doped regions 106 b are treated by a source drain implant 204. The implant 204 may include ion implantation by conventional ion beam, plasma source ion immersion, plasma source ion implantation, and/or other processing techniques. In the present embodiment, the implant 204 may include P-type impurities. In other embodiments, the implant 204 may include impurities such as phosphorous, boron, antimony, arsenic, carbon, germanium, and/or other materials. In furtherance of the present example, the implant is heavier doped than the implant used to create the doped regions 106 a. It is understood that different dopants and/or different dopant concentrations can be used, as desired. Alternatively, the implant 204 may utilize thermal diffusion and/or formation of the doped regions 106 c by SEG, CVD, PVD, ALD, and/or other processing techniques.

The implant 204 is used to form a graded junction, which is illustrated by the creation of doped regions 106 a, 106 b, 106 c and 106 d. The doped region 106 b is a combination of the prior process used to create doped region 106 a and the implant 204. If the prior process and the implant 204 use similar dopants, the doped region 106 b can be comparatively heavier doped than the region 106 a. If dissimilar dopants are used, the doped region 106 b can have a unique combination from the two process steps.

The doped region 106 d, in the present example, is deeper than the previous doped region 106 a of FIG. 5. In one embodiment, the implant 204 uses similar dopants of the prior process used to create doped region 106 a. In this embodiment, the doped region 106 d provides a deeper grading affect. It is understood that although the grading effect is shown as a stair step in FIG. 6, in actuality the grading effect may be more gradual, or smoothed, as shown in FIG. 8.

The doped region 106 c is created by the implant 204 on the epi layer 124. In the present example, the SiGe layer 124 allows the implant 204 to go deeper than that of the doped region 106 d. Furthermore, the resulting properties of the implant 204 on the SiGe layer 124 may be different than those on the Si substrate 102 used for the doped region 102 d. It is understood that in some embodiments, a portion of the implant 204 may extend beyond the epi layer 124 and further into the substrate 102, or in the alternative, may not completely diffuse into the epi layer. It is further understood that although the grading effect is shown as a stair step in FIG. 6, in actuality the grading effect may be more gradual, or smoothed, as shown in FIG. 8.

Referring also to FIG. 7, at step 24 (of FIG. 1) connections are provided to the gate, source, and drain of the transistor device 101, and a clamping layer 118 is formed. In the present embodiment, the connections are made through a gate contact 116 and source/drain contacts 126. The gate contact 116 may include a metal silicide such as cobalt silicide (CoSi_(x)), molybdenum silicide (MoSi_(x)), nickel silicide (NiSi_(x)), titanium silicide (TiSi_(x)), and/or other materials. The gate contact 116 may be formed by lithography, chemical etch, plasma etch, CVD, PECVD, ALD, PVD, and/or other processing techniques. Similarly, the source/drain contacts 126 may be include silicide formed in and/or over the doped region 106 c. The formation of the gate contact 116 and/or source/drain contacts 126 may also include an anneal process step.

The clamping layer 118 or “contact etch stop layer (CES)” may include openings positioned for the gate contact 116. The clamping layer 118 may include silicon nitride (Si_(x)N_(y)), silicon dioxide (SiO₂), silicon oxy-nitride (SiON), silicon oxy-carbide (SiOC), silicon carbide (SiC), and/or other materials. In some embodiments, the clamping layer 118 may be located over the doped regions 106 b and 106 c and include openings positioned for the source/drain contacts 126.

The clamping layer 118 may also provide tensile stress and/or compressive stress which may influence the crystalline stress of the channel region 120. The tensile stress of the clamping layer 118 may be controlled by the process parameters during the formation of the clamping layer 118. Compressive stress may be induced into the clamping layer 118 and may also be controlled by the process parameters. In one embodiment, the clamping layer 118 compressive and/or tensile stress may also be adjusted by temperature, process gas flows, nitrogen content, and/or other process related parameters.

Upon completion of step 24 (of FIG. 1), subsequent processing may be performed to form other features located over the gate contact 116 and the doped regions 106 c, which may include the formation of a metal silicide, a barrier layer such as tantalum nitride (TaN) or silicon oxy-carbide (SiOC), interconnects having copper (Cu) or aluminum (Al), low-k dielectric layers, and or other layers. In one embodiment, the microelectronic device 101 may be annealed thereby forming the “graded junction” between the doped regions 106 b, 106 a, and 106 c (similar to that shown in FIG. 8). The anneal may provide a smooth transition between the impurities of the doped regions 106 b, 106 a, and 106 c.

Referring to FIG. 8, in another embodiment, a complementary microelectronic circuit 300 (also referred to as complementary metal oxide semiconductor (CMOS) circuit) includes a substrate 302, an isolation region 304, microelectronic devices 320 and 322, and clamping layers 316 a, 316 b, and 316 c. The CMOS circuit 300 can by created, in part, by using one or more steps of the method 10 of FIG. 1. It is understood that other steps and/or layers may be created as needed, such is as well known to those of ordinary skill in the art.

The substrate 302 may include one or more of silicon, gallium arsenide, gallium nitride, strained silicon, silicon germanium, silicon carbide, carbide, diamond, and/or other materials. The substrate 102 may also include a silicon-on-insulator (SOI) substrate, such as a silicon-on-sapphire substrate, a silicon germanium-on-insulator substrate, or another substrate including an epitaxial semiconductor layer on an insulator layer. The substrate 302 may further include a fully depleted SOI substrate wherein the device active silicon thickness may range between about 200 nm and about 5 nm in one embodiment. In another embodiment, the substrate 302 may include an air gap to provide insulation for the microelectronic device 300. For example, a “silicon-on-nothing” (SON) structure may be employed wherein the microelectronic device 300 includes a thin insulation layer formed by air and/or other insulator.

The isolation regions 304 may include shallow trench isolation (STI), local oxidation of silicon (LOCOS), and/or other electrical isolation features. The isolation regions 104 may include silicon dioxide (SiO₂), silicon nitride (Si_(x)N_(y)), silicon carbide (SiC), low-k dielectric, and/or other materials. In one embodiment, the isolation region(s) 104 may by etching or otherwise forming a recess in the substrate 302 and subsequently filling with one or more layers of a dielectric.

The microelectronic device devices 320, 322 may also include one or more layers or other features contemplated by the microelectronic circuit 300 within the scope of the present disclosure, and may be formed by immersion photolithography, maskless lithography, imprint lithography, SEG, CVD, PVD, PECVD, ALD, Langmuir-Blodgett (LB) molecular assembly, chemical mechanical polishing or chemical mechanical planarization (hereafter referred to as CMP), and/or other processing techniques. Conventional and/or future-developed lithographic, etching and/or other processes may be employed to form the microelectronic device 100.

The microelectronic devices 320 and/or 322 may include an N-type metal oxide semiconductor (NMOS) device and/or P-type metal oxide semiconductor (PMOS) device, respectively. The microelectronic devices 320 and 322 may include portions substantially similar to the discussions above with respect to the microelectronic device 100. For example, gate layer 308, liners 312, spacers 314, and bulk gate electrode 310 may be substantially similar in composition to the gate layer 108, liners 112, spacers 114 a, and the bulk gate electrode 110 discussed above.

In the present example, the device 322 was formed using an epi layer at the source/drain region, as is discussed above with reference to FIGS. 4–6. In contrast, the device 320 was not formed using an epi layer as described above. As a result, the device 322 includes a three-step graded formation of the dopant regions 306 a, 306 b, 306 c, and 306 d, while the device 320 includes a two-step graded formation of the dopant regions 306 a, 306 b, and 306 d. It is understood that since the devices 320, 322 are not of the same type, different dopants can be used to form the layers 306 a–306 d, such selection of dopants being well understood by those of ordinary skill in the art.

It is generally understood that different embodiments will see different benefits. For example, in some embodiments, a significant current gain will be observed over prior art devices, as well as a lower junction capacitance. Some prior art devices can only provide higher drive current with a higher junction capacitance. This improvement can occur, in some embodiments, without a significant change in threshold voltage.

The foregoing has outlined features of several embodiments according to aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. For example, there are many know ways to form a layer or structure, including deposition, diffusion, implantation, etching, growing, and so forth. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 

1. A method of forming a p-channel transistor on a silicon substrate, comprising: forming a poly gate structure over the substrate; forming a lightly doped source/drain region in the substrate; forming an oxide liner adjacent to opposing side walls of the poly gate structure; forming a wide spacer on opposing side walls of the oxide liner; etching a recess in the lightly doped source/drain region of the semiconductor substrate on opposing sides of the wide spacer; forming raised SiGe source/drain regions in the recesses; partially etching the wide spacer subsequent to forming the raised SiGe source/drain regions to form a slim spacer on opposing side walls of the oxide liner; implanting a source/drain dopant into the substrate including the SiGe source/drain regions; and providing a silicide region in the implanted SiGe source/drain regions.
 2. The method of claim 1 further comprising: forming a hard mask over the poly gate structure prior to forming the raised SiGe source/drain regions; and removing the hard mask after the raised SiGe regions are formed.
 3. The method of claim 2 wherein the hard mask is about 250 Angstroms in thickness.
 4. The method of claim 1 wherein the implanted source/drain SiGe regions are deeper than an implanted region of the substrate that is between the slim spacer and the implanted SiGe source/drain regions, and wherein the implanted SiGe source/drain regions are deeper than the lightly doped source/drain regions under the slim spacer.
 5. The method of claim 1 wherein the wide spacer is about 650 Angstroms in width.
 6. The method of claim 1 wherein the slim spacer is about 350 Angstroms in width.
 7. The method of claim 1 wherein the oxide liner is about 650 Angstroms in width.
 8. The method of claim 1 further comprising: forming a clamping layer over the transistor. 